1. Field of the Invention
The present invention relates to a cursor generating apparatus applicable to computer graphics.
2. Description of the Prior Art
In general, a computer graphics system includes an image memory in which graphics data (whose each bit corresponds to each pixel (picture element) on a display screen) are stored. These graphics data are read from the image memory in raster fashion, converted into video signals, and then applied to a display unit for display of a graphic image.
Conventionally, when a cursor is required to be displayed on an image display in overlap condition, graphics data for displaying a cursor (referred to as cursor data) are formed by a host computer, and the formed cursor data are written in the image memory in overlap condition with graphics data originally stored in the image memory. Therefore, when the cursor is required to be moved, the old cursor data are once erased in the image memory; and then new cursor data corresponding to a new cursor position are formed again; the formed cursor data are written in the image memory; and the above process is repeated.
In the above-mentioned prior-art technique, it has been difficult to move the cursor smoothly at high speed, because it takes much time to form the cursor data and store them in the image memory. Subsequently, in the case of a system in which cursor position is controlled by a mouse, for instance, there exists a problem in that when the mouse is moved at a high speed, the cursor cannot follow the movement of the mouse smoothly, so that the cursor is moved being skipped.